1. Field of the Invention
This invention pertains to pharmaceutical liquid suspension formulations suitable for oral administration In another aspect, it pertains to sustained release suspensions. In yet another aspect, this invention pertains to theophylline formulations.
2. Description of Related Art
Theophylline is an antiasthmatic drug with a narrow therapeutic window. It is available in a number of different dosage forms including conventional tablets, sustained release tablets, elixirs and suspensions. The currently available suspensions settle to the bottom of the container upon standing for several days. If the container is not shaken adequately, the contents will not resuspend in a uniform fashion and the amount of theophylline present per dose will vary.
European Patent Application 0,101,418 (Kallstrand et al.) discloses what is said to be a controlled release pharmaceutical mixture which masks bad taste and increases stability of an active substance, characterized in that an encapsulated active substance is combined with a substance controlling the release of the active substance. The release-controlling substance is a carbohydrate or a carbohydrate-related material and microencapsulated theophylline is among the enumerated actives.
UK Pat. No. GB 2166651B discloses a suspension of pharmasomes containing theophylline. The suspension vehicle consists of (by weight): 85.3% 70% sorbitol solution, 0.7% Avicel RC 591, 0.3% potassium sorbate, 2.7% of a solution containing titanium dioxide 25% in 70% sorbitol, 0.01% simethicone 10% emulsion, 10.8% glycerine, 0.3% citric acid and 0.04% sodium lauryl sulphate.